The aim of the proposed work is the development of a improved power source for the left ventricular assist systems. Phase I showed the feasibility of constructing high volumetric and high gravimetric energy density rechargeable cells based on the lithium/titanium disulfide chemistry. Phase II will focus on the improvement of the rate capability, the cycle life and safety of these cells. In addition, modeling of the cells will be conducted to develop predictive models for long-term behavior based on short-term data. Finally, aspects of cell performance when assembled into multicell battery packs will be investigated.